Temporal changes of warm-season pan evaporation in a semi-arid basin in Western Turkey

Warm-season (from May to September) pan evaporation series recorded at nine sites in semi-arid Büyük Menderes Basin in Western Turkey were analyzed for evidence of long-term changes using non-parametric Mann–Kendall test. Only two sites showed significant linear trends, one in decreasing direction and the other in increasing direction. Area-averaged normalized anomalies of pan evaporation stayed unchanged over the period 1975–2006. Based on correlation and multiple regression analysis with visual inspection of the time series plots, sunshine duration which is used as a proxy for global radiation was found to be the major factor explaining the change and variability of pan evaporation in warm-season in semi-arid Büyük Menderes Basin. Stepwise multiple regression analysis showed no significant effect of rainfall on pan evaporation, which means that the effect of complementary relationship is rather weak and even non-existent.